Mosaic DEM grid layers using SAGA GIS

If an area of interest is covered by multiple digital elevation (DEM) model files, then it may be necessary to mosaic or merge the individual DEM files to create a single DEM grid layer. The Grid Merging command in SAGA GIS can be used to perform this task. 

In this example, I will illustrate importing and merging a few SDTS DEM layers. 

Importing SDTS DEM files

1. Start up SAGA GIS.
   
2. Select Modules | File | GDAL/OGR | GDAL: Import Raster.
   
   The GDAL: Import Raster dialog box appears.
   
   
3. Select the Files row. Click the Browse [...] button.
   
   The Open dialog box appears.
   
   
4. Browse and select a SDTS DEM file, e.g. 9903CATD.DDF. Click Open.
   
   The GDAL: Import Raster dialog box is updated with the selected file.
   
5. Click Okay.
   
   The SDTS DEM layer is imported.
   
6. Repeat steps 2 to 5 for importing the other DEM files of interest.
   
   

Displaying DEM files in one Map window

1. In the Workspace pane on the left, double click one of the imported DEM layer.
   
   The layer is displayed in a Map window.
   
2. Double click on another grid layer.
   
   The Add layer to selected map dialog box appears.
   
   
3. Choose the previously created Map window instead of New. Click OK.
   
   The layer is displayed in the same Map window.
   
4. Repeat 2 to 3 for the remaining grid layers.
   
5. Select Map | Zoom to Full Extent.
   
   All the grid layers can be seen in the same Map window.
   

Merge the DEM layers into one

1. Select Modules | Grid | Construction | Merging.
   
   The Merging dialog box appears.
   
   
2. Select the Grids to Merge row. Click Browse [...].
   
   The Grids to Merge dialog box appears.
   
   
3. On the list on the left, select all the grid layers to merge (while pressing down the CTRL button). Click the >> button.
   
   
   
4. Click Okay.
   
   
   
5. In the Target Grid combo box, choose create.
   
6. If necessary, change the Preferred data storage type, Interpolation, or Overlapping Cells options.
   
7. Click Okay.
   
   The selected grid layers are merged.
   
   
8. In the workspace pane, double click on the merged grid and display in a new Map window.